In many years of teaching (not just Aikido), my experience has been that most "hardship" situations are usually overblown, and can be overcome through a small amount of flexibility and ingenuity on the part of the instructor.

How, specifically, would you handle this one? Particularly, as a concrete scenario, one or two male students and a female student, where one of the males will not train with a female?

How would you handle a one-student class where the student could not be touched by the instructor? (Do you do ki-testing?)

Would these solutions work for you in the long term, or are they short-term only?